Plant components and parts of noble metals, preferably platinum group metal (PGM) materials, are used in the glass industry, especially in plants for fusing and hot-molding special glass.
Platinum Group Metal (PGM) materials are distinguished by their high melting points, by high temperature resistance, and also by high mechanical strength and resistance to abrasion. Therefore they are particularly suitable for making structural parts in plants or parts of plants that come into contact with glass melt. Such suitable materials include platinum and alloys of platinum and/or other platinum group metals, which may optionally also contain lesser proportions of base metals as further alloying components, or oxide additives. Typical materials are refined platinum, PtRh 10 (a platinum-rhodium alloy containing 10% rhodium) or platinum that contains a small proportion of finely divided refractory metal oxide, such as zirconium oxide in particular, to increase strength and increase resistance to high-temperature creep (“FKS (fine-grain-stabilized)” platinum). The same or similar materials are also abbreviated as ODS (Oxide Dispersion Strengthened), DPH (DisPersion Hardened) or ZGS (Zirconia Grain Stabilized) materials. DE-A 2002 886 discloses a possible method to manufacture such materials and its contents and is herewith incorporated by reference. Melt technology plant components, such as those described above, are used for melting, refining, transporting, homogenizing, and measuring out molten glass.
Melt technology plant components are usually made essentially of plates of noble metal, often as thin-walled tube systems. Molten glass flows through them at temperatures between 1000° C. and 1700° C. These tube systems are generally surrounded by ceramic, which both insulates and supports them and which, in turn, is often held by supportive metal structures such as metal boxes.
The PGM parts are made at room temperature and installed in the corresponding plants. They are operated at temperatures in the range of about 1000° C. to 1700° C.
One process step in glass melting is “refining.” “Refining” involves complete dissolution and homogeneous distribution of all the individual components of glass, particularly the elimination of streaks, and refining, i.e., removal of gas bubbles from the melt. Attaining maximum homogeneity and freedom from bubbles requires thorough mixing and degassing of the glass.
For certain special glasses, optical glasses, or even display glasses, refining is done in a PGM tube with a round cross-section. In operation, the tube lies essentially horizontally. The tube is filled half to two thirds full of glass so as to get the best use of the refining chamber, which is made of very expensive material.
The following points, among others, are critical for refining: (a) the size of the open surface of the glass has a substantial effect on the effectiveness of degassing; (b) the maximum path of the rising gas bubbles affects the time required for refining; (c) the mixing and throughput are determined by the flow profile and the velocity of the glass flow; and (d) the temperature of the glass and the temperature distribution in the glass affect the refining. As the refining is done at the highest temperature in the entire glass fusion process, heat is added directly or indirectly to the refining segment.
There is a need for new and improved solutions for melting and hot forming of glass.